The present invention relates to a wheel structure, particularly for cars, having a hub, rim and spoke system, the spoke system having at least one profile element for transmitting forces between the hub and rim.
The term spoke system is here to be understood in the broadest sense and covers all constructional means positioned between the hub and rim and used for transmitting forces between them. The hub is located in the centre of the wheel structure and is the connecting member to the axle structure. It can be substantially fixed to the spoke system and detachably fixed to the axle structure for wheel change purposes, or conversely can be detachably connected to the spoke system and substantially fixed to the axle structure. In addition, parts of the hub can be located on the spoke system and detachably connected with further hub parts on the axle structure. Unless the term rim is placed within inverted commas hereinafter when it also includes at least the spoke system, it is merely understood to mean the outer ring of the wheel, which carries the tire.
The forces acting on wheel structures and their individual components occur radially between the hub and rim as a result of the vehicle weight, as well as the dynamic loads on travelling over unevennesses or potholes. During acceleration and deceleration tangential forces occur between the rim and hub. When taking curves axial forces must be added thereto which attempt to bend the hub and rim out of their parallel position to one another. For the transmission of these forces, particularly the radial forces, elements such as spokes or disks (solid or interrupted) are used. The most varied combinations of these elements have arisen due to the weight, price and ventilation, as well as esthetic effects.
In the car sector the most widely used is the so-called xe2x80x9csteel rimxe2x80x9d, because it is manufacturable in a technically functional and inexpensive manner. However, from the optical standpoint it does not have a particularly attractive appearance. The spoke system, which in the case of steel rims comprises a drawn steel sheet provided with openings or breaks and which is also known as a wheel disk, is consequently generally covered with a hubcap. A hub as a functionally independent part does not have a steel rim. In this case that part of the axle structure to which the steel rim is screwed is generally called a hub.
To an ever increasing extent steel rims are being replaced by so-called xe2x80x9clight metal or alloy rimsxe2x80x9d, because due to the material they have a lower weight, but in particular because the spoke system is or can be designed more attractively from the visual standpoint. In the case of xe2x80x9clight metal rimsxe2x80x9d the spoke system is often constructed in one piece with the rim as a casting. As a design object and as a result of the casting mould required for their manufacture light metal or alloy rims are more expensive than steel rims. A different mould is required for each rim type and each rim size. A new mould is also required for each shape or design change. Therefore the market introduction costs for a new rim type are high.
FR 366,221 and FR 2 676 397 A1 disclose wheel structures having a spoke system with as the carrying element elastically deformable, i.e. resilient rings. As a result of the deformability of the rings the wheels are to be given an internal elasticity or resilience. A wheel structure with a fundamentally similar spoke system is known from U.S. Pat. No. 3,465,304.
Through the invention, as characterized in the claims, a wheel structure with a spoke system is provided which, in the case of an adequate stability, low weight and low material costs, can be easily and inexpensively manufactured, can be easily and widely varied and can be adapted to fashion trends.
The inventive spoke system, according to claim 1, comprises at least one profile element for transmitting forces between the hub and rim, said parts, unlike in the aforementioned, known constructions, being joined together to form an intrinsically stiff structure or, particularly if the hub or parts of the hub are added to the axle structure, can be joined together.
The term xe2x80x9cstiffxe2x80x9d is here understood to mean that the wheel structure is virtually undeformed under the forces and torques acting thereon, or at least no more or not significantly more than is the case with the known xe2x80x9csteel or light metal rimsxe2x80x9d. Unlike in the case of the standard travel strokes of existing cars and which amount to 10 cm in the region of the wheel suspension and still 3 cm in the region of the tire, the allowable deformations are only a few millimeters.
Modern wheel structures are subject to various, usually standardized tests. The most severe of these tests is the rotary bending test, in which the wheel is fixed to a bench and to its hub is fixed an approximately 1 m long bar. The free end thereof is then deflected for a predetermined time in circular manner, whilst applying a clearly defined force. Without the aforementioned stiffness, it would not be possible to pass this test.
The profile elements can advantageously be cut from long solid, half or hollow profile or section bars (so-called semifinished products), which already have the desired cross-sectional shape. By modem separation or cutting methods, such as e.g. laser cutting, this can be performed in such a way that no reworking is necessary. Possible cross-sectional shapes are particularly U or V-shapes, but also disks, rings, polygons and drops, together with combinations thereof. However, the profile elements can also be manufactured from sections of flat profiles or from flat stampings by rolling and/or bending.
Another advantage of using profile elements is the material characteristics thereof. As a result of the manner of their production in injection moulding or extrusion pressing processes, the crystals of the profile elements are uniformly oriented in the profile longitudinal direction. Compared with mouldings, such as e.g. modem xe2x80x9clight metal rimsxe2x80x9d, for which a substantially random crystal structure is typical, profile elements can be subject to higher loads or can be made more slender for the same loading.
The profile element or elements can be easily screwed to the hub and rim, as well as optionally adjacent profile elements. However, they could equally well be riveted to the hub and/or rim and/or to one another, or positively or integrally joined, the latter especially by welding.
The axial faces of the profile elements can be oriented in perpendicular manner and/or with an inclined angle with respect to the wheel axle. They can also be curved with respect thereto. Advantageously said angle changes on wheel fitting, so that an initial tension or preloading occurs in the wheel structure. However, an initial tension in the wheel structure can also be produced in fundamentally the same way during manufacture and can be retained by suitable measures. In particular as a result of an inclined or curved construction, the spoke system can also be adapted to the space requirements of the brake shoes of disk brakes. Several profile elements can be arranged in mutually axially displaced manner in several planes. The axial extension of the profile elements is preferably at least a multiple greater than the wall thickness thereof in the radial and/or circumferential direction.
According to another preferred embodiment the hub is constructed as a replaceable part. This allows adaptation to differently dimensioned mid-centrings of different manufacturers or vehicle types and/or a displacement of the so-called inset without replacing the wheel as a whole, which permits a considerable reduction in the multiplicity of wheel types.
A suitable material for the profile elements is steel or light metal (or a light metal alloy).